I found the paper by the University of California - San Francisco researcher Lydia B. Zablotska et al regarding increased risk of leukemia for Chernobyl cleanup workers even at a low (less than 200 millisieverts) cumulative radiation exposure (see my previous post).
From Environmental Health Perspectives Magazine, advance publications (11/8/2012):
The media report on this paper in Japan is causing anxiety. People are worried that any low level of radiation exposure from the Fukushima I Nuke Plant accident would lead to leukemia, as it has been "proven" by this paper. It seems only Nikkei Shinbun actually cited the radiation exposure levels in the study (less than 200 millisieverts, with over 90% less than 100 millisieverts).
Speaking of "low level radiation exposure", I happened on an old article from June last year by Yomiuri Shinbun that mentions the radiation exposure sustained by Self Defense Force soldiers during two-day work (March 12 and 13 last year) at Fukushima I Nuclear Power Plant, pouring water into the reactors to prevent core melts. Of 12 soldiers who had dosimeters on them, 2 soldiers got 80 millisieverts in 2 days, and 8 others exceeded 30 millisieverts. 8 soldiers didn't even have dosimeters.
Ministry of Defense at that time said there would be no health problem because the exposure was within the limit set by the ministry. What's the limit? 100 millisieverts. For 2 days' work.